The present invention relates to an improved bending machine and an improved roller assembly for use in the machine which reduces scratching when a flat glass sheet is bent into curved glass sheet.
Many techniques for bending glass sheets are known in the prior art. One known technique involves supporting the edge portion of the glass sheet on a horizontally-positioned, contoured perimeter mold having a depressed center portion. When the glass sheet is heated, gravity causes the unsupported center portion to sag to conform to the shape of the mold.
The aforementioned, gravity-fed, glass bending process is slow. It is known to speed up the process by pressing the hot glass between a pair of upper and lower contoured molds instead of depending on gravity to bend the glass sheet. This method is disclosed by, for example, Seymour in U.S. Pat. No. 3,846,104.
Other methods of bending flat glass sheets into curved glass sheets are disclosed by Ritter et al., U.S. Pat. No. 3,476,540, Rougeux, U.S. Pat. No. 3,600,150, and Seymour, U.S. Pat. No. 4,300,935.
Freidel et al., U.S. Pat. No. 5,009,693, incorporated herein by reference, also disclose a novel method and apparatus for bending glass. According to Freidel""s method and apparatus, a glass sheet is heated in an oven on longitudinal rows of fused-silica, mini-rollers until the sheet is softened. When the glass sheet is in condition for bending, the vertical position of the longitudinal rows of rollers is changed to create a desired curved contour. The hot glass sheet sags to conform to the curved contour of the longitudinal rows of rollers. The glass sheet is then quickly conveyed to a quench section of the apparatus.
The quench section also includes longitudinal rows of disc rolls formed into the same curved contour as the rollers in the oven. Quench air tubes support the quench rollers and also function to direct quenching air to the top and bottom surface of the bent glass sheet.
The method and apparatus of Freidel produce high-quality, cost-efficient bent glass sheets. However, when it is necessary to bend the glass sheet into a very deep contour, the outside edges of the glass sometimes get scratched as the glass sags downwardly into the bed of rollers. It is believed that scratching occurs because the glass sheet slides transversely (to the direction of travel of the glass sheets through the oven) downwardly across the corners of the fused silica mini-rollers. Therefore, it would be desirable to provide a vertically-adjustable, roller assembly which will not scratch the glass sheet if the sheet slides transversely across the roller assembly during bending.
The present invention relates to a bending machine and a roller assembly for use in the machine which reduces scratching when bending flat glass sheets into curved glass sheets. The roller assembly generally comprises a base bracket and a bending roller rotatably mounted on the base bracket. The base bracket has a base portion, two horizontally-extending legs, and two vertically-upwardly-extending shoulders.
The bending roller is mounted on two arms which are pivotally-mounted on the shoulders. The bending roller is supported by a bending roller axle which is removably fixed to and extends between the free end of the arms. The arms are supported on an arm pivot axle which is removably fixed to the bracket shoulders.
The bending roller has a three-piece construction. The bending roller has a central hub having an annular outer surface, opposed side surfaces, and a central axis of rotation. The bending roller also has a collar fixed to each side surface of the central hub.
The collars have an annular outer surface, inner and outer side surfaces, and a central axis of rotation. The collars are coaxial with the central hub. The collars are preferably made of a material and made in a shape which will not scratch the glass sheets passing thereover. The scratch resistant material preferably comprises carbon for application temperatures less than 900 F. and boron nitride for application temperatures greater than 900 F.
The central hub has an annular shoulder protruding axially-outwardly from each side of the hub. The collars have an annular recess extending axially-inwardly from the inner side surface of the collar. The shoulder and recess have complimentary shapes so that the collars and the central hub cooperatively engage one another. Each collar has a diameter larger than the diameter of the central hub.
The bending roller includes a set pin extending axially from one collar, through the central hub, and into the second collar. A pinch roller is rotatably mounted between the legs of the base bracket and is constructed and arranged to rotatably contact only the central hub of the bending roller. As the pinch roller drives the central hub, the set pin insures that the collars also are rotated along with the central hub.
The collars have rounded corners at the intersection of the outer annular surface and the outer side surface. This construction helps prevent scratching of the glass sheets.
The roller assembly also includes means for preventing the pivot arm axle from binding on the shoulders due to the buildup of scale over a long period of time. In a preferred embodiment, the means for preventing binding comprises a pair of opposed, open-ended slots in the arms of the bracket in which the pivot arm axle is supported.
The above-described roller assemblies are designed to operate at a temperature not greater than about 900xc2x0 F., above which temperature the carbon collars begin to fail. However, in order to bend glass sheets, the glass sheet must be heated to a softening temperature of about 1300xc2x0 F. Therefore, the present invention provides a novel machine for bending glass sheets using the above-described roller assemblies wherein whereby the temperature in the area of the roller assemblies is maintained below 900xc2x0 F.
The bending machine of the present invention includes a bending chamber housing, conveyor rolls to transport glass sheets to and from the bending chamber, a first and second sets of mini-rolls to support the glass sheet in the bending chamber, means for raising and lowering the first and second sets of mini-rolls, and a means for rotating the mini-rolls and the conveyor rolls. The bending machine also preferably has a pre-heat oven for heating the glass sheet to a softened, bendable condition prior to conveying the glass sheet to the chamber housing.
The chamber housing has an entrance end and an exit end. A plurality of conveyor rolls are located proximate the entrance and exit of the chamber.
The chamber housing preferably has a two-piece hearth construction having an upper portion and a lower portion. The upper portion is constructed and arranged to be raised and lowered relative to the conveyor rolls.
The first set of mini-rolls are constructed and arranged to be raised and lowered along with the upper portion of the housing. The first set of mini-rolls preferably comprises fused-silica mini-rolls.
The mini-rolls of the second set are arranged in longitudinal rows across the width of the chamber. The mini-rolls of the second set preferably have a three-piece construction. The rolls have a central hub having an annular outer surface, opposed side surfaces, and a central axis of rotation. A collar is fixed to each side surface of the central hub. The collars have an annular outer surface, inner and outer side surfaces, and a central axis of rotation. The collars are preferably made of a material and in shape which resists scratching the glass sheets.
The bending machine includes means for raising and lowering each longitudinal row of mini-rolls in the second set to form a desired contour.
An insulation layer is arranged intermediate the first set of mini-rolls and the second set of mini-rolls. The insulation layer divides the chamber into an upper and lower section each of which can be controlled at a different temperature.
Heating means are located in the upper and lower sections of the chamber, and cooling means are located in the lower section. The cooling means preferably comprises a plurality of transversely-extending, elongate, perforated air pipes connected to an air source. The insulation layer is mounted on top of the air pipes. The insulation layer and air pipes are constructed and arranged to be raised and lowered relative to the conveyor rolls.
The bending machine further includes means for controlling the temperature of the chamber in the upper section independent of the temperature in the lower section of the chamber. The control means includes a controller and thermocouples which are located proximate the heating means, cooling pipes, and second set of mini-rolls.
The present invention further includes a method of bending a glass sheet using a plurality of roller assemblies having a maximum operating temperature below the bending temperature of the glass sheet. The glass sheet is initially preheated at a temperature above the bending temperature of the glass sheet. The glass sheet is then conveyed to a heated bending chamber having a plurality of roller assemblies arranged in longitudinal rows supporting the glass sheet. The temperature within the chamber proximate the roller assemblies is maintained as high as possible without exceeding the maximum operating temperature of the roller assembly. The rows of roller assemblies supporting the glass sheet are raised or lowered to a desired contour to bend the glass sheet.